Embodiments of the present invention relate to the encoding and decoding of pictures, for example, still images and video pictures, and in particular to in-loop or post-filtering in such encoding and decoding schemes.
The MPEG-2 video coding standard developed primarily as an extension of prior MPEG-1 video capability with support of interlaced video coding was an enabling technology for digital television systems worldwide. It is widely used for the transmission of standard definition (SD) and High Definition (HD) TV signals over satellite, cable, and terrestrial emission and the storage of high-quality SD video signals onto DVDs. However, an increasing number of services and growing popularity of high definition TV are creating greater needs for higher coding efficiency. Moreover, other transmission media such as Cable Modem, xDSL or UMTS offer much lower data rates than broadcast channels, and enhanced coding efficiency can enable the transmission of more video channels or higher quality video representations within existing digital transmission capacities. Video coding for telecommunication applications has evolved through the development of the MPEG-2 coding standard and later through the development of the MPEG-4 coding standard and has diversified from ISDN and T1/E1 service to embrace PSTN, mobile wireless networks, and LAN/Internet network delivery.
In state-of-the-art hybrid video coding, image quality degradation caused by blockwise coding is reduced by applying an adaptive deblocking filter within the motion-compensated prediction loop, as described by Thomas Wiegand, Gary J. Sullivan, Gisle Bjontegaard, and Ajay Luthra in “Overview of the H.264/AVC Video Coding Standard”, IEEE Tran. on Circuits and Systems for Video Technology, vol. 13, no. 7, pp. 560-576, July 2003, in the following referred to as [1]. The adaptive deblocking filter is applied to the edges of the prediction and/or transform blocks. Thereby blocking artifacts are reduced and both, subjective and objective picture quality can be improved. However, there is still a need to improve the subjective and objective picture quality.